In a Time Division Multiplexing (TDM) Passive Optical Network (PON), such as a Gigabit Passive Optical Network (GPON), an Optical Network Unit (ONU) at the customer premises (or other location) may disrupt an upstream transmission for other customers on the PON. In those circumstances, those skilled in the art typically refer to the ONU as a “rogue” ONU. An ONU goes rogue for a number of different reasons, for example, as when the rogue ONU tries to transmit outside of its allocated timeslot, fails to reduce optical power sufficiently when not transmitting (effectively raising the noise floor for other ONU's) or experiences other technical failures. This rogue condition can result from a hardware/software failure or a malicious attack, for example, from a hacker. Regardless of the cause of a rogue ONU, this condition can potentially disable the entire PON.
The International Telecommunication Union Telecommunication Standardization Sector (ITU-T) community is currently cataloguing methods for detecting and correcting rogue conditions. This community has considered the addition of a “watchdog” circuit to the ONU outside the transceiver to monitor the ONU transmitter and ensure that the ONU complies with instructions from the Optical Line Terminal (OLT), which is typically located at the Central Office (CO). This watchdog circuit shuts down the ONU transmitter after determining that the ONU is exhibiting rogue behavior. In one proposal from ITU-T, a watchdog circuit located outside the transceiver monitors the ONU “transmit enable signals,” used to turn the ONU laser off and on, to detect and enforce ONU compliance. Greater control at the transmitter and closer to the laser, however, is desired.